As is well known, prior art percussion tools have been extensively utilized in the construction and manufacturing fields for such diverse applications as paving breaking, pile driving, impact hammering, and casting deburring. Basically, all prior art percussion tools are characterized by a piston or hammer mounted within a tool casing and adapted to reciprocate under the force of a pressurized working fluid such as air, hydraulic oil, or water to impact a blow striking member such as a chisel point. The actuation of the vast majority of prior art tools has typically been accomplished by various valving mechanisms adapted to alternatively vent and apply the pressurized working fluid to opposite sides the piston.
Although such prior art percussion tools have proven generally effective to accomplish their desired function, they have possessed inherent dificiencies which have detracted from their overall effectiveness in the trade. Foremost of these deficiencies has been the extremely high vibration force communicated to the operator of the tool during reciprocal movement of the piston within the casing. Such vibration force has necessarily caused discomfort to a user during initial use and after prolonged use has often resulted in permanent physical damage to the operator such as white knuckles disease. In addition, conventional prior art pneumatic percussion tools have usually been noisy in operation due to the cyclic venting of high pressure air to the work environment. Further, the operation of such conventional prior art percussion tools has typically been grossly inefficient requiring extremely high input power requirements to effectuate the resultant work product.
Although these deficiencies have recently been recognized to a limited extent in the art, the solutions to date have been directed primarily toward the mere dampening or reduction in the magnitude of sensed vibration in the percussion tool. More recently, it has been discovered that true vibration-free percussion tool operation may be effectuated by use of a constant pressure force being continuously applied to one side of the reciprocating piston against which the piston is alternatively reciprocally driven. Examples of such vibrationless prior art devices based upon this constant pressure force concept are depicted in the following U.S. Pat. Nos. 2,400,650; 2,679,826; 2,730,073; 2,752,889; 2,985,078; 3,028,840; 3,028,841; 3,200,893; 3,214,155; 3,255,832; 3,266,581; 3,291,425; 3,295,614; and 4,290,489; the disclosures of which are expressly incorporated herein by reference.
The most recent tool configuration operating on this vibrationless operation principal is U.S. Pat. No. 4,290,489--Leavell issued Sept. 22, 1981. In the particular percussion tool depicted in this U.S. Pat. No. 4,290,489 patent, vibrationless operation is obtained by use of a constant pressure force working fluid being continuously applied to one side of a reciprocating hammer while noise reduction and increased operational efficiency is provided by effectuation of a substantially adiabatic expansion of the working fluid to atmospheric pressure within the tool. Valving of the working fluid within this particular tool is facilitated by a spring biased pressure actuated poppet which selectively vents and pressurizes the volume disposed on the opposite side of the hammer acting against the constant pressure force.
Although this particular U.S. Pat. No. 4,290,489 tool structure comprises a landmark invention which can only be construed as the current state of the art in vibrationless percussion devices, the tool has proven rather cost prohibitive which has prevented its complete obsolescence of conventional prior art tools in the marketplace. Further, the use of a spring biased pressure activated poppet member has yielded moderate fatigue failure concerns and has somewhat limited the reciprocation frequency or speed of the tool.